GKN1 and obesity due to melanocortin 4 receptor deficiency: In the present study we find that GKN1−/− mice, which are resistant to obesity, have significantly lower levels of Firmicutes or Erysipelotrichia compared to WT mice, indicating that GKN1 plays a role in the development of an obesity-associated gut microbiome and suggests that GKN1 mediates obesity indirectly through effects on the gut microbiome.